My copending application Ser. No. 07/170,299, now U.S. Pat. No. 4,840,704 is directed to controlling filtrate recirculation to obtain a substantially constant average mass of pulp mat on a pulp washing surface. However the distribution of recirculated filtrate is not controlled. This wouldn't matter if the amount of pulp and water across the width of the washing surface were uniform and if the formed pulp mat were dried uniformly but this is not the case because in current practice recirculated filtrate is distributed by a header with slots and baffles which do not accommodate to change in tonnage rates and because in current practice there is inefficient mixing in a cross direction in the headbox and because the apertured drying surface can become clogged in parts.
It is an object herein in one embodiment to control distribution of dilution liquid to obtain more uniform washing operation by the showers that are applied.
It is an object herein in other embodiments to obtain more uniform distribution of one or more of various properties in the pulp mat, e.g., mass of pulp and water, mass of water, dilution factor, displacement factor, dielectric loss, concentration of sulfur and/or sodium.